nushell/crates/nu-std/tests/test_core.nu

use std/assert

#[test]
def banner [] {
    use std/core
    assert ((core banner | lines | length) == 15)
}
Improves startup time when using std-lib (#13842) Updated summary for commit [612e0e2](https://github.com/nushell/nushell/pull/13842/commits/612e0e21602f55092bc121bfd07f7c3bf5119e4f) - While folks are welcome to read through the entire comments, the core information is summarized here. # Description This PR drastically improves startup times of Nushell by only parsing a single submodule of the Standard Library that provides the `banner` and `pwd` commands. All other Standard Library commands and submodules are parsed when imported by the user. This cuts startup times by more than 60%. At the moment, we have stopped adding to `std-lib` because every addition adds a small amount to the Nushell startup time. With this change, we should once again be able to allow new functionality to be added to the Standard Library without it impacting `nu` startup times. # User-Facing Changes * Nushell now starts about 60% faster * Breaking change: The `dirs` (Shells) aliases will return a warning message that it will not be auto-loaded in the following release, along with instructions on how to restore it (and disable the message) * The `use std <submodule> ` syntax is available for convenience, but should be avoided in scripts as it parses the entire `std` module and all other submodules and places it in scope. The correct syntax to just* load a submodule is `use std/<submodule> ` (asterisk optional). The slash is important. This will be documented. `use std ` can be used for convenience to load all of the library but still incurs the full loading-time. `std/dirs`: Semi-breaking change. The `dirs` command replaces the `show` command. This is more in line with the directory-stack functionality found in other shells. Existing users will not be impacted by this as the alias (`shells`) remains the same. * Breaking-change: Technically a breaking change, but probably only impacts maintainers of `std`. The virtual path for the standard library has changed. It could previously be imported using its virtual path (and technically, this would have been the correct way to do it): ```nu use NU_STDLIB_VIRTUAL_DIR/std ``` The path is now simply `std/`: ```nu use std ``` All submodules have moved accordingly. # Timings Comparisons below were made: * In a temporary, clean config directory using `$env.XDG_CONFIG_HOME = (mktemp -d)`. * `nu` was run with a release build * `nu` was run one time to generate the default `config.nu` (etc.) files - Otherwise timings would include the user-prompt * The shell was exited and then restarted several times to get timing samples (Note: Old timings based on 0.97 rather than 0.98, but in the range of being accurate) \| Scenario \| `$nu.startup-time` \| \| --- \| --- \| \| 0.97.2 ([aaaab8e](https://github.com/nushell/nushell/commit/aaaab8e070c644a87bbd7682099e3fe9e6a4b42a)) Without this PR \| 23ms - 24ms \| \| This PR with deprecated commands \| 9ms - <11ms \| \| This PR after deprecated commands are removed in following release \| 8ms - <10ms \| \| Final PR (remove deprecated), using `--no-std-lib` \| 6.1ms to 6.4ms \| \| Final PR (remove deprecated), using `--no-config-file` \| 3.1ms - 3.6ms \| \| Final PR (remove deprecated), using `--no-config-file --no-std-lib` \| 1ms - 1.5ms \| These last two timings point to the opportunity for further optimization (see comment in thread below (will link once I write it). # Implementation details for future maintenance * `use std banner` is a ridiculously deceptive call. That call parses and imports all of `std` into scope. Simply replacing it with `use std/core ` is essentially what saves ~14-15ms. This only* imports the submodule with the `banner` and `pwd` commands. * From the code-comments, the reason that `NU_STDLIB_VIRTUAL_DIR` was used as a prefix was so that there wouldn't be an issue if a user had a `./std/mod.nu` in the current directory. This does not appear to be an issue. After removing the prefix, I tested with both a relative module as well as one in the `$env.NU_LIB_DIRS` path, and in all cases the internal `std` still took precedence. * By removing the prefix, users can now `use std` (and variants) without requiring that it already be parsed and in scope. * In the next release, we'll stop autoloading the `dirs` (shells) functionality. While this only costs an additional 1-1.5ms, I think it's better moved to the `config.nu` where the user can optionally remove it. The main reason is its use of aliases (which have also caused issues) - The `n`, `p`, and `g` short-commands are valuable real-estate, and users may want to map these to something else. For this release, there's an `deprecated_dirs` module that is still autoloaded. As with the top-level commands, use of these will give a deprecation warning with instructions on how to handle going forward. To help with this, moved the aliases to their own submodule inside the `dirs` module. * Also sneaks in a small change where the top-level `dirs` command is now the replacement for `dirs show` * Fixed a double-import of `assert` in `dirs.nu` * The `show_banner` step is replaced with simply `banner` rather than re-importing it. * A `virtual_path` may now be referenced with either a forward-slash or a backward-slash on Windows. This allows `use std/<submodule>` to work on all platforms. # Performance side-notes: * Future parsing and/or IR improvements should improve performance even further. * While the existing load time penalty of `std-lib` was not noticeable on many systems, Nushell runs on a wide-variety of hardware and OS platforms. Slower platforms will naturally see a bigger jump in performance here. For users starting multiple Nushell sessions frequently (e.g., `tmux`, Zellij, `screen`, et. al.) it is recommended to keep total startup time (including user configuration) under ~250ms. # Tests + Formatting * All tests are green * Updated tests: - Removed the test that confirmed that `std` was loaded (since we don't). - Removed the `shells` test since it is not autoloaded. Main `dirs.nu` functionality is tested through `stdlib-test`. - Many tests assumed that the library was fully loaded, because it was (even though we didn't intend for it to be). Fixed those tests. - Tests now import only the necessary submodules (e.g., `use std/assert`, rather than `use std assert`) - Some tests thought they were loading `std/log`, but were doing so improperly. This was masked by the now-fixed "load-everything-into-scope bug". Local CI would pass due the `$env.NU_LOG_<...>` variables being inherited from the calling process, but would fail in the "clean" GitHub CI environment. These tests have also been fixed. * Added additional tests for the changes # After Submitting Will update the Standard Library doc page 2024-10-03 13:28:22 +02:00			`use std/assert`

			`#[test]`
			`def banner [] {`
			`use std/core`
			`assert ((core banner \| lines \| length) == 15)`
			`}`